NO340056B1 - Method and apparatus for determining and managing saturation in a wireless communication system - Google Patents

Description

Method and apparatus for determining and managing saturation in a wireless communication system

The present invention relates to the field of wireless communication. More specifically, the present invention relates to Wireless Local Area Network (WLAN) systems that utilize Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanisms and provide means to determine and manage saturation and further improve network management, by providing new medium access control (MAC) measurements in wireless communication.

Wireless communication systems are well known in the art. In general, such systems include communication stations that send and receive wireless communication signals among themselves. Depending on the type of system, communication stations are typically one of two types: base stations or wireless transceiver units (WRTUs), which include mobile devices.

The term base station, as used herein, includes, but is not limited to, a base station, hub B, area controller, access point, or other interface device in a wireless communications environment that provides WTRUs with wireless access to a network with which the base station is associated.

The term WTRU, as used herein, includes, but is not limited to, a user equipment, a mobile station, fixed or mobile user device, pager, or any other type of device capable of operating in a wireless environment. WTRUs include personal communication devices, such as telephones, videophones, and Internet-ready telephones that have network connectivity. In addition, WRTUs include portable personal computing systems, such as PDAs and notebook computers with wireless modems, which have corresponding networking capabilities. WRTUs that are portable or otherwise capable of changing location are referred to as mobile devices. Usually base stations are also WRTUs.

A network base station is typically provided where each base station is capable of operating simultaneous wireless communication links with suitably configured WRTUs. Some WRTUs are configured to operate wireless communication with each other, that is, without being relayed through a network via a base station. This is usually called peer-to-peer wireless communication. Where a WTRU is configured to communicate with other WTRUs, it may itself be configured as and operate as a base station. WTRUs can be configured for use in multiple networks with both network and peer-to-peer communication capabilities.

One type of wireless system, called a wireless local area network (WLAN), can be configured to operate wireless communications with WTRUs equipped with WLAN modems that are also capable of operating peer-to-peer communications with similarly equipped WTRUs . Currently, WLAN modems are integrated into many traditional communicating and data processing devices by manufacturers. For example, mobile phones, personal digital assistants and laptop computers are built with one or more WLAN modems.

A popular local area network environment with one or more WLAN base stations, typically called access points (APs), is built according to the IEEE 802.11 family of standards. An example, the 802.11 Local Area Network (LAN), as shown in Figure 1, is based on an architecture where the system is further divided into cells. Each cell includes a Basic Service Set (BSS), which includes at least one AP for communication with one or more WTRUs commonly referred to as stations (STAs) in the context of 802.11 systems. Communication between an AP and STAs is conducted according to the IEEE 802.11 standard that defines the air interface between a wireless STA and a wired network.

A wireless LAN (WLAN) can be formed by a single BBS, with a single AP, which has a portal to a distribution system (DS). However, installations are typically assembled with multiple cells and APs are linked together through a backbone network, referred to as a DS.

A mobile ad-hoc network (MANET) is also shown in Figure 1. A MANET is a self-configuring network of mobile routers (and associated hosts) interconnected by wireless links - and this interconnection forms an arbitrary topology. The routers are free to move randomly and organize themselves arbitrarily; so that the topology of the network can change rapidly and unpredictably. Such a network can operate independently or can be connected to the wider Internet.

An interconnected WLAN, including the various cells, the respective APs and the DS, is considered a single IEEE 802.11 network and is referred to as an Extended Service Set (ESS). IEEE 802.11 networks typically use a "Carrier-Sense Multiple Access / Collision Avoidance" (CSMA/CA) protocol to exchange information wirelessly between nodes (or STAs) in the WLAN network. In this framework, STAs wishing to transmit must contend for access to the wireless medium. The contention mechanism involves waiting for the medium to remain idle for a certain time interval (according to a set of rules prescribed by the standard) before sending a data packet. The time it takes for a node to access the channel and send its packet increases as the number of stations and data traffic increases. Saturation in such a system can occur when the time taken to access the medium becomes unacceptable due to too many stations contending for the same medium.

Due to the nature of the CSMA/CA protocol and the consideration that most transmissions are of the best attempt type, it is very difficult to determine when a system is classified as detecting saturation. Determining saturation in such a complex system is no easy task, since one choice of measurement method would indicate saturation while another measurement method would not.

Several measurement methods can be used to indicate saturation and include: collision frequency, channel utilization, i.e. the time the medium is occupied, and so on. However, these measurement methods, used individually, will not necessarily give a true picture of saturation. For example, the channel utilization measurement does not give an accurate picture of the saturation situation. A station can be alone on a channel and broadcast all the time. In this case, the channel utilization metric would be high. It would appear that the system would not be able to support any more traffic from other stations. However, if a new station were to join the channel, it would still experience good capacity due to the nature of the CSMA/CA mechanism, because the channel would then be equally shared between the two stations. A system is actually in saturation when there are a number of stations contending for the same channel at any given time and experiencing large delays due to the increasing amount of time each station has to wait for access to the medium, as well as the greater number of collisions .

In another aspect, network management functionality is now limited, particularly in systems conforming to the IEEE 802.11 and IEEE 802.1lk standards. Investors have recognized that there are certain limitations to the usefulness of the channel load information that is used in the state of the art in connection with network administration. There is also a need for an improved method to achieve better network management after considering the limitations of using channel-load measurements. The present invention provides improved network management associated with the IEEE 802.11 and IEEE 802.11c standards in connection with channel load information.

An example can be found in EP 1156623.

The present invention provides a method for determining and announcing saturation in a wireless local area network (WLAN) system. The present invention also provides a method for administering saturation when saturation is detected. One aspect of the present invention relates to wireless systems that use CSMA/CA. Preferably, multiple measurement methods are used to determine saturation including: average duration of backoff procedure, "in-Basic Service Set" (in-BSS) delay rate, "out-of-BSS" delay rate, number of associated stations, average WTRU channel utilization and average buffer "Medium Access Control" (MAC) usage. Actions taken to alleviate the saturation situation preferably include; to sort the collection of WTRUs in order of most wasted time spent sending acknowledged/unacknowledged packets and disconnect each WTRU, one at a time, until the saturation is resolved.

The present invention also provides an improved method for network management, particularly in the context of the IEEE 802.11 and IEEE 802.1lk standards, preferably by using two (2) new MAC measurements. Specifically, the two (2) new measurements include the STA uplink traffic load measurement and an "Access Point" (AP) service load measurement.

The invention includes assessments of the management information base (MIB) representation in the send queue size which provides a new measurement of the STA send load in the sense of unserved traffic demand in queue. The invention further includes assessments of the MEB representation of the AP service load which provides a new measurement of the AP service load to be used to assist STAs with handoff decisions. Realization of these features can be done by software or by any suitable means. This aspect of the invention is generally applicable, for example to layers 1 and 2, as used in a system in accordance with IEEE 802. liki in the context of orthogonal frequency division multiplexing (OFDM) and code division multiple access 2000 (CDMA 2000) systems. However, the invention is generally applicable in other scenarios as well.

The procedures can advantageously be realized in selected configured WTRUs in various designs.

A more detailed understanding of the invention can be obtained from the following description of the preferred embodiments, given by means of examples and to be understood in connection with the attached drawings. Figure 1 is an overview diagram of conventional IEEE 802.11 WLANs with their corresponding components. Figures 2-9 are flowcharts illustrating the present invention's techniques for determining saturation and managing saturation in wireless communication systems. More specifically, Figures 2 and 2A together present a method for determining saturation using deferral rate (DR) and packet error rate (PER) metrics and disassociating WTRUs based on determination of wasted time attempting to transmit. / resend, not approved packages. Figure 3 presents a procedure for managing load planning by comparing the load of a node with announced loads from neighboring nodes. Figure 4 presents a method for providing announced load to WTRUs based on the average delay from a packet reaching the start of a queue to transmission of the packet. Figures 5, 6 and 7 present a method for providing the size of the transmission queue (TQS), the size of the conflict-free transmission queue (CFTQS), respectively the size of the conflict transmission queue (CFTQS) to neighboring nodes. Figure 8 presents a method, used by a node, for managing a channel based on evaluation of served and unserved traffic load from WTRUs and for providing a numbered level for announcement to WTRUs. Figure 9 presents a procedure used by WTRUs to select a node based on load level provided by neighboring nodes. Figure 10 is a diagram of a BSS payload format according to the present invention. Figure 11 is a diagram of an access category service payload element format according to the present invention.

Figure 12 a communication station configured according to the present invention.

Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element may be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention.

One aspect of the present invention introduces two different approaches to determining load measurement for channel saturation; first a Basic Service Set (BSS)-based load measurement, which is primarily based on the individual AP's load. Then a channel-based load measurement, which is a measurement that indicates the load that is shared between different APs.

BSS-based load measurement are values that determine conditions with high load and channel saturation. The two preferred BSS-based load measurements are: in-BSS delay rate measurement and packet error rate measurement.

Delay Rate (DR) is a measurement that represents the percentage of time that the AP's receiver has a locked carrier (that is, "Clear Channel Assessment" (CCA) indicates a busy condition) while the AP has one or more packets to transmit ( that is, its queue is not empty). In other words, DR represents the amount of time that the AP spends delaying transmission to other WLAN nodes.

In-BSS Deferral Rate "Deferral Rate" represents the percentage time that the AP's receiver is locked to an in-BSS packet (that is, a packet originating from one of its associated WTRUs) while the AP has one or more packages to send. In other words, the in-BSS DR represents the amount of time that the AP spends delaying its own transmissions because one of its associated WTRUs has taken control of the medium (that is, transmits a packet).

In-BSS deferral rate "Deferral Rate" indicates at what level the current load is in a system and when there is a need to send measurement of the time used to defer a transmission to another node. A low measured in-BSS delay rate indicates that the load to the BSS is low. A high in-BSS delay rate indicates that there are many nodes transmitting at the same time and that there is therefore a significant load.

In a case where there are only two nodes in the system with a significant amount of data to send, the delay rate can be high and if used alone will indicate saturation. However, because there are only two nodes in the system, this would not be considered a saturation situation. To account for this situation, the packet error rate (PER) is used in addition to the delay rate measurement. The packet error rate (PER) is the ratio between the number of failed transmissions (that is, packet transmissions where an ACK was not received) and the number of packets sent. The PER measurement is a good indication of the collision rate in the system when conservative data transmission rates are used. The greater the number of nodes in a system, the greater the probability of collision. The use of both measurement of in-BSS exposure rate and PER measurement together provides a better indication of the load of an AP than either measurement used alone.

In the present invention, as shown in Figure 2, the in-BSS delay rate and PER respectively are determined in steps S1 and S3 and are then equalized over a predetermined time period (for example 30 seconds) in steps S2 and S4 respectively. The averages in both measurements are used to inform about the occurrence of saturation in steps S5 and S6. More specifically, when the in-BSS delay rate (DR) measurement exceeds a first predetermined threshold, determined in step S5, and the PER measurement exceeds a second predetermined threshold, determined in step S6, over a given period (for example, 30 seconds) , then this is an indication of saturation.

Whether saturation is determined based on the criteria set forth above or not, or by using other techniques for determining saturation, the present invention provides the following actions; first, in step S7, the AP sorts all the WTRUs in the "Basic Service Set" (BSS) in the order of the amount of time used to try to retransmit. Wasted time is preferably determined according to the wasted time algorithm ALGwt described below. Specifically, a set or list of WTRUs with unacknowledged packets is formed. For each unacknowledged packet to a WTRU, the sum of all wasted time spent attempting to send and retransmitting the packet (that is, packet size / packet transmission rate plus a penalty for each packet retransmitted) is recorded. The penalty reflects the increasing delay associated with the retransmissions, i.e. the backoff time due to the doubling of the saturation window (CW). The penalty represents the additional delay incurred from the time the packet was ready to be sent to the time the packet was actually sent over the medium. The measured retransmission time is therefore much greater for stations that waste time retransmitting packets after collisions have occurred. The target for the retransmission time is normalized over a selected time interval.

An example of a formula for determining wasted time for a WTRU is given by:

The present invention also provides for the use of other measurements including: BSS-based measurements; the number of associated WTRUs, the time at which the access point "Access Point" (AP) receives all acknowledgments (ACKS) (eg fragmentation) related to this packet in "medium access control"

(MAC), and the average buffer MAC usage (based on the size of the buffer).

The present invention further provides a method that takes into account the load of neighboring APs in its assumption of the system's need to perform some load sharing (that is, disassociation) or load balancing. For example, if, as shown in Figure 3, the load of each of the neighboring APs is also large, as collected in steps S9 and S10, and compared to neighboring APs in steps Sil and Sl2, the load planning is delayed (step Sl4) because the user had a low probability of being served elsewhere, that is, LI, L2 and L3 are all large (step S13). The load planning is controlled in step S26 if LI or L2 have lower announced loads (step S15B). If the L3 load is less than LI and L2, the AP can accept a WTRU, as shown in steps S15A and S17.

In order to announce load to its stations (WTRUs), an access point (AP) can compare its load with respect to neighboring APs, i.e. for example AP(x) and AP(y). When an AP load is high compared to the estimated load of its neighboring APs, then the AP announces a high load in response to a determination in step S15A (Figure 3). When the AP load is low compared to the estimated load of its neighbors, the AP will announce a low load in response to a determination in step S15B.

Another method used in the present invention is to use measurement specifications that determine the medium's (ie the channel's) load. This measurement specification enables the WTRU to select the AP with the least load. Media load indications are used in cases where in-BBS channel load is not effective, such as the case where a BBS with an in-BSS channel load simply defers to a neighboring BSS and therefore, even if the load of the AP is low, the medium's load is high. In this case, the announced load could represent the medium's load. In this case, an AP only announces low load when it is able to support the new WTRU.

A metric that gives an indication of the media load is the average duration (AvgD) required to perform the backoff procedure determined in the manner shown in Figure 4 for downlink transmission in an AP. Specifically, this metric represents the medium's access delay from the time a packet is ready for transmission (that is, CSMA/CA access contention begins) to the time the packet begins to be transmitted over the medium in steps S28-S23 and announce AvgD to the WTRU -es in step S24.

The size of the match window affects the duration required to perform the backoff procedure. The match window size increases when an acknowledgment is not received from the receiving node. This relationship covers cases where collisions occur either between nodes in the same BSS or other BSSs. During the countdown of a backoff procedure, the countdown stops when it detects that the media is busy, increasing the duration of the backoff procedure. This additional aspect covers the cases where the medium has a high load due to WTRUs in the own BSS and/or neighboring BSSs. This measurement alone provides a good indicator of the saturation as perceived by this node in the BSS. One could simply consider using the time that the medium is occupied (channel utilization) as a measurement value. However, in an example where only one WTRU is associated with the access point (AP) and is sending or receiving large amounts of data, the channel utilization value will not give a good indication of saturation. The channel utilization will indicate heavy saturation when in reality the system is only serving one user. A second user (WTRU) being added to this AP could easily be supported. In the single user example, the new proposed AvgD metric (that is, the average duration to perform the backoff procedure) would correctly indicate low saturation.

AvgD measurement is a preferred measurement since a short required duration for the backoff procedure indicates a lightly loaded medium, while a long duration indicates a heavily loaded medium. As an example, consider the current IEEE 802.1 lb standard. The minimum value for a combat window (CW) is 32x20[is = 640 u.s and the maximum value is 1023x20 us = 20.5 ms. However, the duration required to perform backoff may be greater than the maximum size of the CW, caused by the stoppage of the countdown due to the perception of a busy medium. This increase in duration will give an indication of load due to the activity in the medium.

The reasons for the use of MAC load measurements in the context of the present invention include: The MAC layer has a lot of information which in the state of the art is not available via the management information base (MEB) or via measurements in the standards IEEE 802.11 and IEEE 802. Ilk.

New information units provided by the present invention, which are useful to the upper layers, are not available in the prior art although they can be provided within the scope of IEEE 802.Ilk.

IEEE 802.Ile has identified channel utilization, "identified channel utilization" (CU), as a useful load information unit.

The present invention recognizes the need for WTRU uplink load information and AP service load information. Some of the limitations of CU information include: Loading information useful for handover decisions in the WTRU and AP. CU information about a potential target AP is useful to the WTRU when evaluating handover options. CU is the sum of uplink served load (all WTRUs to AP) and downlink served load (AP to all WTRUs), also known as channel utilization.

Traffic load, however, consists of two parts: serviced traffic load and unattended traffic load (queuing).

In the state of the art, CU does not provide dynamic, unattended traffic load information in queues.

In the state of the art, the network has no way of accessing unserved uplink traffic needs (traffic load in queue).

The benefits of WTRU uplink traffic loading measurements (UTML) in network management include:

A large channel load indicates that served traffic is close to its maximum.

If unattended traffic demand is low, this is optimal channel management.

If unattended traffic demand is high, this is sub-optimal.

Unattended uplink traffic demand is extremely useful to enable an AP to better share uplink and downlink segments in frame time.

APs need to manage the channel for maximum traffic utilization and minimal traffic blocking.

Uplink traffic queuing in WTRUs indicates transmission delays and potential channel blocking. The volume of data queued in MAC transmission buffers provides a good measure of uplink queue load.

The present invention provides a new MAC management information base (MAC MIB) element for transmit traffic load, called Transmit Queue Size (TQS). Transmit Queue Size (TQS) is defined as follows. New MEB information includes three (3) units: total transmit queue size (TQS), which consists of the sum of contention-free TQS (CFTQS) and contention TQS (CTQS).

TQS holds the current MAC queue size in bytes. TQS can be included in a MAC MIB 802.11 counter table "Counters Table". "DotllCounters Table" is a defined data structure in the standard. TQS information may be implemented by a counter as shown in Figure 5, the WTRU initializes, in step S25, the TQS counter to zero at system startup. The WTRU receives, in step S26, a frame and, in step S27, places the frame into the MAC layer. In step S28, the WTRU increments the TQS counter by the number of bytes in the queued frame. Alternatively, the accumulation can be done with a software technique where a count step can be stored in a memory and incremented by replacing a current count (PC) with, say, PC+1, as each byte in the frame is queued.

The WTRU sends, in step S29, a frame using the physical layer (PHY) when a session is initiated and decrements the TQS counter by the number of bytes sent, either when operating in non-acknowledgment mode or when a frame is acknowledged by an AP after the PHY transmission. The WTRU communicates, in step S31, the TQS count to neighboring APs. TQS is a new MEB element. All MD3 items are sent to neighbors as needed via a MEB request that is executed to retrieve an item from a neighbor's MD3.

The content transmit queue size (CTQS) is realized, for example as shown in Figure 6, where the WTRU initializes, in step 32, the CTQS counter to zero at system startup. The MAC layer of the WTRU receives, in step S33, a contention window and, in step S34, adds it to the contention queue of the MAC layer. In step S35, the CTQS counter is incremented by the number of bytes in the received frame.

The WTRU transmits, in step S36, the frame (for example to an AP) using the PHY layer whether operating in unacknowledged mode or when the frame has been acknowledged after PHY transmission and decrements, in step S37, the CTQS the counter with the number of bytes sent, whether operating in unacknowledged mode or when the frame has been acknowledged after a PHY transmission. In step S38, the WTRU communicates the CTQS count to neighboring APs.

The conflict-free transmission queue size (CFTQS) is realized, as shown in Figure 7, by providing a CFTQS counter where the WTRU, in step S39, initializes the CFTQS counter to zero at system startup.

In step S40, the WTRU-MAC layer receives a contention-free frame and, in step S41, queues the frame in the contention-free queue (CFQ). In step S42, the WTRU increments the CFTQS counter by the number of bytes in the queued frame.

In step S43, the WTRU transmits a saturation-free frame using the PHY layer and, in step S44, decrements the CFTQS counter by the number of bytes sent in the frame in unacknowledged mode or when the frame has been acknowledged after the PHY layer transmission. In step S45, the WTRU communicates the count to neighboring APs.

Figure 8 shows a way in which an AP utilizes MAC-MD3 information where, for example, in steps S46, S47 and S48 respectively, the AP receives MAC-MIB information including one or more of the TSQ, CTQS and CFTQS counts, for example from WTRU(x), WTRU(y) and WTRU (z). This data, which represents unserved traffic, is combined with served traffic data such as channel load, which includes both uplink and downlink load and is evaluated by the AP in step S49 and utilizes, in step S50, the served and the unserved load data for to manage the channel, for example by adjusting traffic to maximize traffic utilization and minimize traffic congestion. The AP can adjust uplink and downlink segments of frames, based on unattended uplink traffic data, in order to optimize channel utilization.

The considerations for providing AP service load measurements in the context of the invention include the following: WTRUs may consider multiple APs as target APs for handover. If two APs have similar channel load and acceptable signal quality, the WTRU needs an opportunity to be able to determine which AP is the best. By making available to APs subsequent information regarding their ability to serve their existing set of WTRUs and their ability to serve other WTRUs, channel usage can be optimized. This information corresponds to a downlink traffic queue measurement for the AP modified by any AP-specific information regarding its assumed capacity.

The following applies to AP service load:

a new MAC-MD3 information unit is provided to assist WTRUs in their handover decisions.

A quantitative indication on a scale of 255 values (e.g. represented by 8 binary bits), from "currently no WTRU is being served" to "cannot handle any new services" with a defined midpoint indicating that the service load is optimal. For example:

0 == Do not operate any WTRU (an AP or an idle WTRU is no AP)

1 through 254 == scalar indication of AP service load.

255= unable to accept any new service.

Exact specification of this MEB unit is implementation dependent and does not need to be specified with absolute accuracy; a detailed definition to achieve maximum utility can be tailored to the characteristics of the particular network.

The new AP service load may be included in MAC dotl 1 counter tables or elsewhere in the MEB.

A WTRU that has multiple APs that can be selected as the target AP, in addition to an assessment of channel load and acceptable signal quality, as shown in Figure 9, can receive load indications from AP(x), AP(y) and AP(z ), shown in steps S51, S52 and S53, and, in step S54, evaluates the received AP announced loads (SL scalars) and is thus able to make a decision based on comparisons of the announced and received AP loads and, in step S55, selects an AP.

The AP service load (SL) is a scalar value and can be based, for example, on served and unserved traffic, as well as other data, such as signal quality and assumed capacity, based on, for example, statistical data. The AP-SL scalar may be formed as shown in step S50A of Figure 8 and announced to neighboring WTRUs as shown in step S50B.

The above methods are preferably realized in selectively configured WTRUs. For example, a WTRU may be configured to assist in channel management in a wireless network by providing a memory device, a processor, and a transmitter. The memory device is preferably configured to provide a queue of data frames to the medium access control (MAC) layer of the WTRU. The processor is preferably configured to determine queue size data for access points (APs) in the wireless network whereby a receiving AP utilizes the queue size data to assist with channel management. In particular, the processor is configured to initialize to zero a count representing the size of queued data at system startup and to increment the count by a number of bytes in a frame when the frame is queued by the medium access control (MAC) layer of the WTRU . Preferably, the processor is configured to decrement the count by a number of bytes in a frame when a frame is sent by the physical (PHY) layer of the WTRU in an unacknowledged mode. Alternatively, the processor can be configured to decrement the count by the number of bytes in a frame, when a frame is sent by the physical layer of the WTRU when the frame has been acknowledged after a PHY transmission.

In such a WTRU, the memory is preferably configured with contention and contention-free queues in the medium access control (MAC) layer and the processor is configured to determine contention send queue size data (CTQS) representing demand for unattended traffic queued to the contention-free queue and total transmit size data (TQS) representing unattended traffic demand in queue for all the transmit data queues of the medium access control (MAC) layer.

Such a WTRU preferably also includes a receiver configured to receive formulated service load indicators from APs, based on queue size data received from WTRUs by the APs and a controller configured to select an AP for wireless communication based on the received load indicators .

An access point (AP) may be provided configured to provide channel management in a wireless network to both access points (APs) and wireless transceiver units (WTRUs) capable of communicating wirelessly with the APs over wireless channels. A receiver is configured to receive unattended traffic demand data received from WTRUs located within the service range of the AP. The AP preferably has a processor configured to calculate a service load indicator based on unserved traffic demand data received from WTRUs. A transmitter is included that is configured to announce the service load indicator to WTRUs within the AP's wireless service range where WTRUs located within the AP's wireless service range can use the announced service indicator to assist in selecting an AP with which to associate manage wireless communications. In such an AP, the receiver is preferably configured to receive announced service load indicators from other APs and the processor is preferably configured to use the announced service load indicators received from other APs to assist in decisions regarding disassociation of operationally associated WTRUs from communication with the AP.

In another embodiment, a wireless transceiver unit (WTRU) is configured to manage saturation in a wireless communication system defined by a base service station (BBS). The WTRU has a processor configured to determine an in-base service station (in-BSS) delay rate (DR) and average said DR over a given time interval. Preferably, the processor is configured to also determine packet error rate (PER) and average said PER over said time interval. A memory is configured to store comparable values that reflect wasted time spent attempting to send data for each of the WTRUs operatively associated with the WTRU in the BSS. A transceiver configured to disassociate operationally associated WTRUs from the WTRU starting with a WTRU having a stored comparable value reflecting the longest time spent attempting to transmit data, when said average DR and said average PER is greater than given thresholds are included.

In such a WTRU, the processor is preferably configured to average the DR and the PER over a time interval on the order of thirty seconds and the transceiver is configured to periodically receive and update the memory with comparable values that reflect wasted time spent attempting sending data for each WTRU operationally associated with the WTRU.

In such a WTRU, the processor may also be configured to determine a comparable wasted time value by measuring the time it takes the WTRU to receive either a successful acknowledgment (ACK) or negative acknowledgment (NACK) in response to a sent data packet, summing the measured the times over a signal period and normalize the sum over the signal period. The transceiver is then preferably configured to periodically transmit the current comparable values that reflect wasted time spent attempting to transmit data to other WTRUs.

An access point AP may also be configured to assist wireless transmit/receive stations (WTRUs) in selecting an access point AP with which to manage wireless communication in a wireless communication system by providing it with selectively configured components. Preferably, a receiver is configured to receive announced load indicators belonging to other APs. A processor is included which is configured to compare a communication load belonging to other APs and to determine an adjusted load for the AP based on said comparison. A transmitter is configured to announce the adjusted AP load to WTRUs. Preferably, the processor is configured to periodically perform said comparison and determine operations for the purpose of updating the load that the transmitter announces to WTRUs.

In such an AP, the transmitter can be configured to announce a new load when the processor determines that the communication load of the AP is low compared to the announced load of other APs, and to announce a large load when the processor determines that the communication load of the AP one is high compared to the announced load of other APs. The processor can also be configured to determine the communication load of the AP by measuring the delay between the time from when a data packet is ready to be sent and the time when the packet is actually sent to a WTRU, averaging said delay over a given time and utilizing the average the delay to indicate load.

In another embodiment, a base station is configured to disassociate WTRUs from operational association using this when a saturation condition is detected in a wireless network. The base station has a processor configured to determine the wasted time (Tw) used to attempt to send/retransmit unacknowledged packets to each associated WTRU and to normalize the wasted time Tw for each associated WTRU over a given time period. A memory is provided configured to store a list of associated WTRUs and their respective normalized wasted times. A transceiver is configured to disassociate WTRUs to facilitate said saturation, based on their respective normalized wasted times, where a WTRU having a largest Tw is disassociated first. Preferably, the processor is configured to add a penalty to said Tw representing increasing delay associated with retransmissions, such as by being configured to calculate wasted transmission time (Tw) for WTRUs according to the formula set forth above.

IEEE 802.Ile supports multiple access categories, such as voice, video, best effort, and background traffic. In one embodiment, the present invention utilizes AP service load per access category. The BSS load element includes information about the current station's population, traffic level and service level in the BSS. Figure 10 shows an example of an element information field according to the present invention.

The length field must be set to the number of octets in the following fields. The station count field is interpreted as an unsigned integer indicating the total number of STAs currently associated with this BSS. The station count field shall not be represented in signal or probe response frames if, by way of example only, "dotllQoSOptionlmplemented", "dotllQBSSLoadlmplemented" and "dotllRadioMeasurementEnabled" are all "true".

The channel utilization field is defined as the percentage time the AP perceived the medium as busy, as indicated by either the physical or virtual "carrier sense" mechanism. This percentage is represented as a moving average of ((channel-occupied-time/(dotllChannelUtilizationBeaconIntervals<*>dotl lBeaconPeriod<*>1024))<*>255), where channel-occupied-time is defined as the number of microseconds during which "carrier sense " mechanism indicated a channel-busy indication and dotllChannelUtilizationBeaconlntervals represents the number of consecutive beacon intervals during which the average should be calculated. The channel utilization field shall not be represented in signal or probe-response frames if dotl lQoSOptionlmplemented, dotl lQBSSLoadlmplemented and dotllRadioMeasurementEnabled are all "true".

AP service load shall be a scalar indication of the relative service load on an AP. A low value should indicate greater available service capacity than a high value. The value 0 shall indicate that this AP is currently not serving any STA. The values between 0 and 254 shall be a logarithmically scaled representation of the average medium access delay for DCF-sent packets measured from the time the DCF packets are ready for transmission (that is, CSMA/CA access begins) until the relevant packet transmission start time. A value of 1 should represent a 50 uS delay while a value of 253 should represent a 5.5 mS delay or any delay greater than 5.5 mS. The value 254 shall indicate that no additional AP service capacity is available. The value 255 shall indicate that the AP service load is not available. The AP must measure and average the medium access delay for all transmission packets by using the DCF access mechanism over a predetermined time window, such as a thirty second measurement window. The accuracy of the average medium access delay shall be +/- 200 u.S or better when averaged over at least 200 packets.

Access category (AC) service payload elements can be provided in the BSS payload only in QoS-enhanced APs (QAPs). The AC service load shall be a scalar indication of the average access delay (AAD) in a QAP for services of the indicated access category type. A low value should indicate a shorter access delay than a higher value. The value 0 shall indicate that this QAP is currently providing services of the indicated AC. The values between 0 and 254 shall be a logarithmically scaled representation of the average access delay for transmitted packets in the indicated AC measured from the time the EDCF packet is ready for transmission (that is, CSMA/CA access begins) until the relevant packet transmission start time. A value of 1 should represent a 50 uS delay while a value of 253 should represent a 5.5 mS delay or any delay greater than 5.5 mS. The value 254 shall indicate that services on the indicated AC are currently blocked or suspended. The value 255 shall indicate that the AP service load is not available.

The QAP shall measure and average medium access delay for all transmit packets of the indicated AC using EDCF access mechanisms over a predetermined time window, such as a continuous thirty-second measurement window. The accuracy of the average medium access delay shall be +/- 200 u.S or better when averaged over at least 200 packets. The AC service payload is preferably formatted as shown in Figure 11, as two octet sub-elements with the first octet containing the AC indication (ACI) and the second octet containing the measured value of the AAD of the indicated AC. It should be noted that the octets shown in Figures 10 and 11 are provided as an example only and that other octets may be used. Table 1 shows an example of ACI coding.

With reference to Figure 12, a communication station 100 is shown which is configured according to the present invention. It should be noted that communication station 100 may be an access point (AP), a WTRU, or any other type of device capable of operating in a wireless environment. Communication station 100 also includes a processor 104. Processor 104 is preferably coupled to receiver 102 and is configured to calculate a BSS payload for each of a plurality of access technologies. Communication station 100 includes a transmitter 106. The transmitter 106 is preferably configured to announce the BSS payload element within the service range 108 of the communication station 100. The BSS payload element can then be received by other communication stations (for example, access points and/or WTRUs ) within the service range 108 of the communication station 100 and thereby provide them with information regarding the BSS.

Embodiments

1. Method for providing channel management in a wireless network for optimizing network utilization for both access points (APs) and wireless transceiver units (WTRUs) capable of communicating wirelessly with each other on wireless channels, characterized by providing a service load indicator for a first AP for each access category. 2. Method according to embodiment 1 further characterized in that by announcing the service load indicator to WTRUs within the service range of the first AP. 3. The method of any prior embodiment further characterized by selecting an AP with the WTRU based on tj single load indicator one. 4. Method in any of the previous embodiments characterized in that the service load indicator is an indicator of temporary access delay in the first AP. 5. Method according to embodiment 4, characterized in that the average access delay is measured in a predetermined time period. 6. Method according to embodiment 5, characterized in that the time period is thirty (30) seconds. 7. Method in any previous embodiment characterized in that the access categories include voice, video, "best effort" and/or background traffic. 8. Method according to any of the previous embodiments further characterized by receiving the announced service load indicator from a second AP. 9. Method according to embodiment 8, further characterized by using the announced service load indicator in the second AP in the decision to disassociate WTRUs. 10. Method according to any one of embodiments 8-9, characterized in that the second AP disassociates WTRUs with the second AP where the service load indicator from the first AP is small compared to the service load indicator determined by the second AP one. 11. Access point (AP) configured to provide channel measurement according to the method of any of the preceding embodiments. 12. AP according to embodiment 11, characterized in that a processor is configured to calculate a service load indicator for each access category. 13. The AP of any preceding embodiment characterized in that a transmitter configured to announce the service load indicator to WTRUs within the AP wireless service range. 14. The AP of any prior embodiment wherein WTRUs located within the AP's wireless service range may use the announced service load indicator to assist in selecting an AP with which to perform wireless communication. 15. The AP of any preceding embodiment characterized in that a receiver is configured to receive announced service load indicators from other APs. 16. The AP of any preceding embodiment, characterized in that the processor is configured to use the announced service load indicators received from other APs to assist the AP in decisions regarding disassociation of WTRUs. 17. Wireless transceiver unit (WTRU) configured to provide channel management in a wireless network according to a method of any of the preceding embodiments. 18. WTRU according to embodiment 17 characterized by the data receiver for receiving a service load indicator for each access category from an AP. 19. The WTRU according to any one of the embodiments 17-18, characterized in that a processor configured to utilize the service load indicator in the selection of an AP with which to perform wireless communication. 20. Method for providing channel management in a wireless network in order to optimize network utilization by means of communication stations that are able to carry out wireless communication with each other on wireless channels, characterized in that a first communication station provides a "basic service set" (BSS) load element for each of a plurality of access categories. 21. Method according to embodiment 20 further characterized in that by announcing the BSS load element to other communication stations within the service range of the first communication station. 22. Method according to any one of the embodiments 20-21, further characterized in that at least one communication station selects another communication station with which to communicate based on the BSS load element. 23. Method according to any one of the embodiments 20-22, characterized in that the BSS load element includes an element identification field. 24. Method according to any one of the embodiments 20-23, characterized in that the BSS load element includes a communication station, AP or a WTRU service load field, where said communication station, AP or WTRU service load field is a scalar indication of the relative level of service load at a first communication station. 25. Method according to any one of the embodiments 20-24, characterized in that the BSS payload element includes a length field whose value is set to the total number of octets included in all the fields of the BSS payload element. 26. Method according to any of the embodiments 20-25, characterized in that the BSS load element includes a station count field, where said station count field is an unsigned integer indicating the total number of communication stations that are associated with the BSS in question. 27. Method according to any one of the embodiments 20-26, characterized in that the first communication station is a "quality of service" (QoS)-enhanced communication station (QCS) or QoS-enhanced AP (QAP). 28. Method according to embodiment 27, characterized in that said BSS load element further includes an access category (AC) service load field, where said AC service load field is formatted as four subfields, each of which provides a scalar indication of an average access delay ( AAD) at QCS or QAP for the services of one of the access categories. 29. Method according to embodiment 28, characterized in that the AC service load field is included in the BSS load element only if a QoS option realized parameter is "true". 30. Method according to any of the embodiments 28-29, characterized in that the four subfields include an AAD as "best-effort" (AADBE) field, an AAD as background (AADBG) field, an AAD as video (AADVI) - field and/or an AAD as voice (AADVO) field. 31. Method according to any one of embodiments 28-30, characterized in that a low AAD value indicates a shorter access delay than a higher AAD value. 32. The method of any one of embodiments 28-31, further characterized in that by setting an AAD value to the first of the four subfields the AAD value of the subfield adjacent and to the right of said first subfield reaches neither QCS nor QAP provides services for the indicated access category. 33. Method according to any of the previous embodiments, further characterized by measuring and/or averaging a medium access delay (MAD) value of all transmission packets in the indicated access category. 34. Method according to embodiment 33, characterized in that said MAD value is measured and/or averaged using an EDCF mechanism over a continuous time window, where an averaged MAD has a predetermined accuracy range and is based on a minimum number of transmit packet delay measurements. 35. Method according to embodiment 34, characterized in that said time window is a thirty (30) second measurement window, where the predetermined accuracy range is two hundred (200) uS, and/or said MAD average is based on at least two hundred transmission packet delay measurements. 36. Method according to any one of embodiments 28-35, characterized in that an AAD value within a predetermined range of values in one of the four subfields is a logarithmically scaled representation of an average MAD for transmitted packets in the indicated access category, wherein said average MAD is measured from the time an EDCF packet is ready for transmission to the time the EDCF packet is actually sent. 37. Method according to embodiment 36, characterized in that said range of values is between zero (0) and two hundred and fifty-four (254). 38. Method according to any one of the embodiments 28-37 characterized in that the predetermined AAD value in any one of the four subfields indicates that a QCS or QAP does not provide services to the indicated access category or to any higher priority access category. 39. Method according to embodiment 39, characterized in that said predetermined AAD value is zero (0). 40. Method according to any one of embodiments 28-39, characterized in that other predetermined AAD values represent different averaged MAD times. 41. The method of any one of embodiments 28-40, wherein the AAD value of one (1) represents an average MAD of fifty (50) u.S. 42. The method of any one of embodiments 28-41, characterized in that an AAD value of two hundred and fifty-three (253) represents an average MAD of five and one-half (5.5) uS or more. 43. The method of any one of embodiments 28-42, characterized in that an AAD value of two hundred and fifty-four (254) indicates that the services of the indicated access category are currently blocked. 44. The method of any one of embodiments 28-43, characterized in that an AAD value of two hundred and fifty five (255) indicates that the indicated AC service load is not available. 45. Method according to any previous embodiment characterized in that the BSS load element further includes a channel utilization field. 46. Method according to embodiment 45, characterized in that said channel utilization field constitutes the percentage time until the first communication station perceives the transmission medium as being busy, as indicated by a carrier wave detection mechanism. 47. Method according to embodiment 46, characterized in that the percentage time is a moving average. 48. Method according to embodiment 47, characterized in that the moving average is defined by using at least one parameter selected from the group consisting of a busy-channel-time parameter, a channel-utilization-signal-interval parameter and/or a signal-period parameter . 49. Method according to any one of embodiments 47-48, characterized in that said moving average is defined as the product of the busy-channel-time parameter and two hundred and fifty-five (255), divided by the product of the channel-utilization-signal-interval parameter, the signal period and one thousand and twenty-four (1024). 50. The method of any one of embodiments 48-49 characterized in that the busy-channel-time parameter is defined as the number of microseconds that the carrier detection mechanism has indicated channel-busy indication. 51. Method according to any one of the embodiments 48-50, characterized in that the channel utilization signal interval parameter is defined as the number of consecutive signal intervals for which the average can be calculated. 52. The method of any one of embodiments 48-51 characterized in that the channel utilization field is included in the BSS load element when at least one of a QoS option-realized parameter and a PBSS load-realized parameter is "false". 53. A method for determining the medium-access-delay (MAD) time for simple access to a communication station, where the method is characterized by determining the first time when a data packet is ready for transmission. 54. Method according to embodiment 53, characterized in that said first time is a time at which the "Carrier-Sense Multiple Access / Collision Avoidance" (CSMA/CA) protocol is initiated. 55. Method according to any one of the embodiments 53-54 characterized by determining the second time at which a transmission request is made to the physical (PHY) layer transmission process. 56. Method according to any one of the embodiments 53-55 characterized by determining the third time at which said transmission request is confirmed. 57. Method according to any one of the embodiments 53-56 characterized by calculating the packet transmission and confirmation time as the difference between the second time and the third time. 58. Method according to any one of the embodiments 53-57 characterized by calculating the total access time as the difference between the third time and the first time. 58. Method according to any one of the embodiments 53-58 characterized by calculating the MAD time by subtracting the packet transmission and acknowledgment time from the total access time. 59. Method according to any one of the embodiments 53-59, characterized in that the transmission request is preceded by a "Request-to-Send/Clear-to-Send" (RTS/CTS) handshake.

60. Procedure for determining the MAD time for retransmission of data packets.

61. Method according to embodiment 60, characterized by determining the first time at which a data packet arrives at the "medium access control" (MAC) queue. 62. Method according to any one of the embodiments 60-61 characterized by determining the second time at which the data packet is first in the MAC queue. 63. The method of any one of embodiments 60-62, characterized by calculating the MAC queue delay as the difference between the second time and the first time. 64. Method according to any one of the embodiments 60-63 characterized by determining the first retransmission time as the difference between the first transmission start time and the first transmission end time. 65. Method according to embodiment 64, characterized in that said first transmission start time indicates the beginning of the first transmission of the data packet and that said first transmission end time indicates the end of said first transmission without receiving any transmission confirmation 66. Method according to any of the embodiments 60-64 characterized by determining the second retransmission time as the difference between the second transmission start time and the second transmission end time. 67. Method according to embodiment 64 characterized in that said second transmission start time begins after a delay and "back-off" period and indicates the start of the second transmission of the data packet and that said second transmission end time indicates the end of said second transmission without receive any transmission confirmation. 68. Method according to any one of embodiments 60-67 characterized by determining the Nth retransmission time as the difference between the Nth transmission start time and the Nth transmission end time. 69. Method according to embodiment 64 characterized in that said Nth transmission start time begins after a delay and "back-off" period and indicates the start of the Nth transmission of the data packet and that said Nth transmission end time indicates receipt of a transmission confirmation. 70. Method according to any one of the embodiments 60-69 characterized by calculating the total retransmission time as the sum of the first, second and Nth retransmission time. 71. Method according to any one of the embodiments 60-70 characterized by determining an end time, where said end time indicates the time when the confirmation is received. 72. Method according to any one of the embodiments 60-71 characterized by calculating the MAD time of the data packet as the difference between the end time and the start time, minus the MAC queue delay, minus the total retransmission time, all divided by N. 73. Method according to any one of the embodiments 20-52, characterized in that the first communication station is an access point (AP) and where the properties of the BSS load element are configured to be used in and/or by a

AP.

74. Method according to any of the embodiments 20-53, characterized in that any of the other communication stations is an AP. 75. Method according to any one of embodiments 20-54, characterized in that the first communication station is a WTRU and wherein the characteristics of the BSS payload are configured for use by a WTRU. 76. Method according to any of the embodiments 20-55, characterized in that any of the other communication stations in and/or with a WTRU. 77. Method according to any one of the embodiments 53-72, characterized in that the communication station is an AP. 78. Method according to any one of the embodiments 53-72 characterized in that the communication station is the WTRU. 79. Communication station configured to provide channel management according to any of the methods of embodiments 20-53 and 73-76. 80. Communication station according to embodiment 79, characterized in that a receiver is configured to receive unattended traffic demand data from other communication stations located within the wireless service range of said communication station. 81. The method of any one of embodiments 79-80, characterized in that a processor is configured to calculate the BSS payload element of each of the plurality of access categories. 82. Method according to any one of the embodiments 79-81, characterized in that a transmitter is configured to announce the BSS payload element to other communication stations within the service range of said communication station. 83. Method according to any one of embodiments 79-82, characterized in that the receiver is configured to receive announced BSS payload elements from other communication stations. 84. Method according to any one of embodiments 79-83 characterized in that the processor is further configured to utilize the received BSS payload elements from other communication stations to assist communication stations in making disassociation decisions. 85. Method according to any one of the embodiments 79-84, characterized in that said communication station is an AP. 86. Method according to any one of the embodiments 79-84, characterized in that said communication station is a WTRU. 87. Method according to any one of the embodiments 79-86, characterized in that any one of the other communication stations is an AP. 88. Method according to any one of embodiments 79-87, characterized in that any one of the other communication stations is a WTRU. 89. Communication station configured to determine medium access delay according to any of the methods and/or features of embodiments 53-72 and 77-78. 90. Method according to embodiment 89, characterized in that said communication station is an AP. 91. Method according to embodiment 89, characterized in that said communication station is a WTRU. 92. Method according to any one of embodiments 90-91, characterized in that a processor configured to determine the medium access delay according to any one of the methods and/or features of embodiments 53-72 and 77-78. 93. Method for determining the average MAD time evaluated over a predetermined time period characterized by defining the time period. 94. Method according to embodiment 93, characterized by determining the total packet transmission duration by summing the packet transmission time and the time spent waiting for and/or receiving confirmation of the quantity of packet transmissions occurring over said time period. 95. Method according to any one of embodiments 93-94, characterized in that the packet transmissions include packet retransmissions. 96. The method of any one of embodiments 93-95 characterized by determining the total idle transmit queue time of a plurality of access categories. 97. Method according to any one of the embodiments in 96, characterized in that the total empty transmission queue time includes the time periods during which the transmission queues of the access categories remain empty. 98. The method of any one of embodiments 93-96 characterized by subtracting the total packet transmission duration, the total idle transmit queue time and/or the total transmit queue delay time from the duration to arrive at the total difference. 99. The method of any one of embodiments 93-97 characterized by dividing the total difference by the number of packet transmissions to obtain the average MAD time.

100. Method according to any one of the embodiments 93-99 characterized by determining the total transmission queue delay time of the plurality of access categories, where said transmission queue delay time includes time periods during which the access categories postponed their respective transmissions to higher priority queues.

101. Method according to embodiment 100, characterized by subtracting said total transmit queue delay time from the total difference before dividing said total difference by the number of packet transmissions to arrive at the average MAD time.

102. Communication station characterized in that it is configured to determine the MAD time according to any of the methods and/or features of embodiments 93-101.

103. Communication station according to embodiment 102, characterized in that by a processor.

104. Communication station according to any of the embodiments 102-103, characterized in that said communication station is an AP.

105. Communication station according to any of the embodiments 102-103, characterized in that said communication station is a WTRU.

106. Communication station characterized in that it is configured to perform any of the methods and/or features in any of the preceding claims and/or including any described in any of the preceding claims.

107. Communication station according to embodiment 106, characterized in that said communication station is an AP.

108. Communication station according to embodiment 106, characterized in that said communication station is a WTRU.

Although this invention has been specifically shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that the various changes in execution and details can be made within this without leaving the scope of the invention as described above.

Claims (27)

1. Procedure for an access point (AP), characterized by to generate a basic service set, BSS, load element including a plurality of access categories, AC, service load elements, one for each of a voice AC, video AC, "best effort" AC, and a background AC, each of the plurality of AC service load elements indicating a respective AC and one of: a scaled representation of an average access delay for an indicated AC, that a service for the indicated AC is currently unavailable, or that an average access delay for the indicated AC is not available; and sending the BSS load element to a plurality of wireless transceiver units, WTRUs. 2. Method according to claim 1, characterized in that the average access delay is measured in a predetermined time period. 3. Method according to claim 2, characterized in that the time period is thirty, 30, seconds. 4. Method according to claim 1, characterized in that the BSS load element includes 4 octets, and "best effort" AC, background AC, voice AC, and video AC are each a different octet of the 4 octets. 5. Method according to claim 1, characterized in that a value less than 253 in one of the AC service load elements indicates a scaled representation of an average access delay for the corresponding AC. 6. Method according to claim 1, characterized in that a value of 253 in one of the AC service load elements indicates a delay greater than a threshold. 7. Method according to claim 1, characterized in that a value of 254 in one of the AC service load elements indicates that a service for the corresponding AC is currently unavailable. 8. Method according to claim 1, characterized in that a value of 255 in one of the AC service load elements indicates that an average access delay for the corresponding category is not available. 9. Access point, AP, characterized by including: a processor configured to generate a basic service set, BSS, load element including a plurality of access categories, AC, service load elements, one for each of a voice AC, video AC, "best effort" AC, and a background AC, each of the plurality of AC service load elements indicates a respective AC and one of: a scaled representation of an average access delay for an indicated AC, that a service for the indicated AC is currently unavailable, or that an average access delay for the indicated AC not available; and a transmitter configured to transmit the BSS payload to a plurality of wireless transceiver units, WTRUs. 10. AP according to claim 9, characterized in that the receiver is configured to receive the BSS load element from other APs. 11. AP according to requirement 9, characterized in that the average access delay is measured in a predetermined time period. 12. AP according to claim 11, characterized in that the time period is thirty, 30, seconds. 13. AP according to requirement 9, characterized by that the BSS load element includes 4 octets, and "best effort" AC, background AC, voice AC, and video AC are each a different octet of the 4 octets. 14. AP according to claim 9, characterized in that a value less than 253 in one of the AC service load elements indicates a scaled representation of an average access delay for the corresponding AC. 15. AP according to claim 9, characterized in that a value of 253 in one of the AC service load elements indicates a delay greater than a threshold. 16. AP according to requirement 9, characterized in that a value of 254 in one of the AC service load elements indicates that a service for the corresponding AC is currently unavailable. 17. AP according to claim 9, characterized in that a value of 255 in one of the AC service load elements indicates that an average access delay for the corresponding aC is not available. 18. Wireless Transmit/Receive Unit, WTRU, characterized by including: a receiver configured to receive a basic service set, BSS, load element including a plurality of access categories, AC, service load elements, one each of a voice AC, video AC, "best effort" AC, and a background AC, each of the plurality of AC service load elements indicates a respective AC and one of: a scaled representation of an average access delay for an indicated AC, that a service for the indicated AC is currently unavailable, or that an average access delay for the indicated AC is not available . 19. WTRU according to claim 18, characterized in that a value less than 253 in one of the AC service load elements indicates a scaled representation of an average access delay for the indicated AC. 20. WTRU according to claim 18, characterized in that a value of 253 in one of the AC service load elements indicates a delay greater than a threshold. 21. WTRU according to claim 18, characterized in that a value of 254 in one of the AC service load elements indicates that a service for the indicated AC is currently unavailable. 22. WTRU according to claim 18, characterized in that a value of 255 in one of the C service load elements indicates that an average access delay for the indicated AC is not available. 23. Method for a wireless transmit/receive device (WTRU), characterized by to receive a basic service set, BSS, load element including a plurality of access categories, AC, service load elements, one for each of a voice AC, video AC, "best effort" AC, and a background AC, each of the plurality of AC service load elements indicating a respective AC and one of: a scaled representation of an average access delay for an indicated AC, that a service for the indicated AC is currently unavailable, or that an average access delay for the indicated AC is not available. 24. Method according to claim 23, characterized in that a value less than 253 in one of the AC service load elements indicates a scaled representation of an average access delay for the indicated AC. 25. Method according to claim 23, characterized in that a value of 253 in one of the AC service load elements indicates a delay greater than a threshold. 26. Method according to claim 23, characterized in that a value of 254 in one of the AC service load elements indicates that a service for the indicated AC is currently unavailable. 27. Method according to claim 23, characterized in that a value of 255 in one of the AC service load elements indicates that an average access delay for the indicated AC is not available.